This invention relates in general to magnetic tape recorder/players and more particularly to a magnetic tape recorder/player having a low power magnetic tape reel motor and brake assembly.
Magnetic tape recorders/players are widely used to recorder analog or digital information on magnetic tape. Generally, the magnetic tape is transported between magnetic tape reels, past a magnetic head assembly. Each reel is rotated by a motor to transport tape at different speeds. Various brake arrangements have been proposed to bring a motor to a stop. In a magnetic tape recorder, it is desirable, that a brake assembly for stopping a reel motor, be disengaged from the motor during tape transport, but be engaged with the motor, when a stop mode is selected or when power is unexpectedly cut off to the motor. Proper braking prevents excess tape to be thrown off the reels. With the ever increasing demand for smaller tape transports, it is also desirable that a reel motor and brake assembly be compact, reliable and uncomplex in design. It is also desirable that the brake be automatically disengaged when the motor is started and engaged when electrical power to the motor is terminated.
Various techniques have been proposed which use additional electrical power for disengaging a brake upon actuation of a motor. One type of electromagnetic brake is disclosed in U.S. Pat. No. 2,536,491, issued Jan. 2, 1951, Inventors Chapman et al and U.S. Pat. No. 4,477,743, issued Oct. 16, 1984, Inventors Apetrei et al. As disclosed in these patents, additional stator and rotor windings are provided to effect an electromagnetic disengagment of a, spring biased, normally engaged, brake when power is applied to the motor. Such a technique is complex, expensive and wasteful of electrical power. Another electromagnetic technique utilizes an externally mounted solenoid which is actuated, when power is supplied to the motor, to disengage a normally engaged brake. U.S. Pat. No. 1,639,038, issued Aug. 16, 1927, Inventor Jobst and U.S. Pat. No. 3,651,899, issued Mar. 28, 1972, Inventor Yoshii, disclose devices which are illustrative of this technique. This technique is disadvantageous because of its waste of power and space and because of its complexity.
In order to minimize the waste of power inherent in electromagnetically actuated brakes, it has been proposed to utilize the reactive force exerted on the stator of a motor, when it is energized, to disengage a normally engaged brake. Such a technique is disclosed, for example, in U.S. Pat. No. 2,037,735, issued Apr. 21, 1936, Inventor Oberhoffken and British Patent No. 551,319, issued Feb. 17, 1943, Inventor King. Although the mechanical arrangements disclosed in these patents minimizes the waste of power inherent in electromechanical arrangements, the disclosed arrangements are relatively complex and wasteful of space. Thus, in the former patent, a bulky disk brake is disengaged by movement of the stator by means of a complex and expensive ball bearing ring mounted between cam plates. Similarly, in the latter British patent, the disclosed brake mechanism is either an expensive disk brake or a nipper post brake (FIGS. 3 and 4) and the brake disengagement device is an expensive and bulky cam arrangement.